Add BatchMetricsQueryHandler and tests

Add RollupTestUtils
Refactor plot request parsing logic into its own class
Change MetricData to also contain 'type' of metrics
Changes to serializers for JSON output
Add HTTP endpoint & handler for batched metrics
fix merge conflicts in master pom
Catch-all function to set the value of an `AbstractRollupStat`.
bug fix: Variance.toString() should trigger a compute if necessary.
core parts from cd7ada5

TimerRollup extends BasicRollup. This is temporary.
pre-aggregated column family.
Introduce CounterRollup and some tests.
fix openjdk erasure problems.
fix merge conflict
fix merge conflicts in SerializationTest
fix merge conflicts
should have been committed in last batch.
oops. include preaggregation table in truncation list.
Bug Fix: run compute before checking variance equality.
TimerRollup.toString() still reflected that it extended BasicRollup.
fix merge conflicts